docs(core): add markdown document outlining contribution guidelines

[caleywoods]

This is the start of a markdown document that outlines the guidelines for contributing. I recently submitted my first pull request and I hadn't read the contributing document on the Onivim website, it's a little bit buried in there. I wanted to open this up for discussion before I spent the time copying all of the guidelines into the document.

I think having this would go a long way towards helping new contributors like myself adhere to the requested guidelines. If rehashing the contribution guidelines here isn't wanted since it duplicates things, then I think it should at least be considered that a contributing.md document be pulled in or created that kindly asks contributors to take a moment to read the guidelines already present on the website.

[CrossR]

Any opinions on having the PR specific stuff in an actual PR template : https://docs.github.com/en/github/building-a-strong-community/creating-a-pull-request-template-for-your-repository?

I.e. if its there, when you open a PR it auto populates the box with the contents of that file.

[caleywoods]

Any opinions on having the PR specific stuff in an actual PR template : https://docs.github.com/en/github/building-a-strong-community/creating-a-pull-request-template-for-your-repository?

I.e. if its there, when you open a PR it auto populates the box with the contents of that file.

That could work too! I was just thinking that this document would be that after it gets configured as such inside GitHub but there is a lot that would be listed. I think your idea might be the better approach to just have the PR template outline the desired format and have something maybe at the bottom of it linking to the bigger document on the website.

[caleywoods]

@CrossR I've updated the verbiage to put the important stuff at the top. The document still seems like it would be fairly daunting so I don't think it should grow anymore. Do you see any opportunities to shrink it?

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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